Piston Interface Corer

Long (2.0m long/drive), undisturbed cores of sediment- water interface from shallow lakes

Ideal sampler for gyttja, clay, and fine sand sediments

Literature available on piston coring lake sediments for paleoecological analysis is extensive (see review by Blomqvist 1991). The corer shown here is a simplified composite of proven samplers described in the literature cited below.

Some of these features include:

polycarbonate core tubes

(7.5 cm I.D., 3 mm wall; max 2.0m long)

clear, unbreakable, non-metal sample containment

1.0 cm scribe marks, chamferred edges

piston assembly;

double, integral "O"-rings

built-in vacuum breaker that allows the piston to be withdrawn from the core tube with minimal sediment disturbance and therefore enabling transportation of intact cores

drive/extrusion rod

designed to incrementally expell sediments (see Core Extruding Apparatus) and adjust the piston assembly tension at any point in the tube

this feature allows cores to be extruded from the "top- down" or "bottom up" since the core head can be removed and attached to either side of core tube

internal piston rod

(not shown; see Cushing and Wright, 1965)

deep (>2.0m), consecutive cores may be collected with use of an internal rod which slides through the the drive rods from the surface to the piston assembly

this rod assures the piston remains at the bottom of the core tube until the sampling depth is reached

General Procedure

rinse polycarbonate core tube and piston assembly with water

loosen piston assembly and insert in core tube with cable attached

slide core tube on to core head and tighten hose clamps on "no-hub coupler"

use drive/extrusion rod to push piston assembly to the lower end of core tube and tighten piston assembly (tight enough to be difficult to move by hand) in core tube with the key on end of extrusion rod

retract drive/extrusion rod and secure in place with retainer pin

determine the depth of water and couple the necessary extension rods together

lower the corer to just above the sediment-water interface with slack in the wire. (Figure 1, A)

tie the piston wire to the coring platform.

drivers should place their hands at various levels along the drive rod so that the push can be steady for a full meter without pause

(note: a pause during a drive may prevent furthur recovery since internal core friction may cause plug formation and core compaction)

if driving becomes difficult, it may be nessasry to use pipe wrenches or cross beams to provide mechanical advantages (Figure 1, B)

pull the corer from the sediments while maintaining tension on the piston cable (if cable slips, part of the core may be lost) (Figure 1, C)

cap the bottom of the core tube with polyethylene caps (or bottom piston when extruding from the "bottom-up") until the extrusion process begins.

Notes: The piston assembly and thin wall core barrels collect, high quality, uncompressed samples. Upon retrieval, one must plug the bottom of the core tube before breaking the air-water interface (with core extruding plug or poly end cap) to prevent loss of sample.

Clear polycarbonate core barrel material readily available at most plastic distributors. Core extruding plugs allow one to incrementally extrude sediments upward with aid of a Core Extruding Apparatus. Core barrels can easily be drilled/plugged (for pore water extraction), serrated, cut and split to meet the special needs of the investigation.